Thin-film rechargeable batteries have numerous applications in the field of microelectronics. For example, thin-film batteries provide active or standby power for microelectronic devices and circuits. Active power sources of the thin-film battery type are used, for example, in implantable medical devices, remote sensors, miniature transmitters, smart cards, and MEMS devices. Standby power sources of the thin-film battery type are used, for example, in PCMCIA cards and other types of CMOS-SRAM memory devices.
In a thin-film battery, a chemical reaction takes place between an anode and cathode by interaction of the anode and cathode through an electrolyte. The attractiveness of thin-film batteries over conventional batteries is that the electrolyte is a substantially solid or non-flowable material rather than a liquid. Liquid electrolytes pose leakage problems and are often highly corrosive. Of the solid electrolytes, thin-film batteries typically employ organic and ceramic electrolytes. Solid electrolytes are desirable in cells or batteries where liquid electrolytes may be undesirable, such as in implantable medical devices. Preferred solid electrolytes include materials that are solid at room temperature, electrically insulative and ionically conductive.
Examples of solid electrolytes include metallic salts and vitreous solid compositions. Metallic salt solid electrolytes include, for example, compounds that conform to the formula: AgI-MCN—AgCN, wherein M is potassium, rubidium, cesium or mixtures thereof. Vitreous solid compositions, or glasses, are generally comprised of a network former, a network modifier and, in those cases where the network modifier does not provide a mobile cation, a network dopant. A network former provides a macromolecular network of irregular structure. A network modifier is an ionic compound that becomes incorporated into the macromolecular network of the network former. A network dopant provides mobile cations to the network.
As advances are made in microelectronic devices, new uses for thin-film batteries continue to emerge. Along with the new uses, there is a need for high performance thin-film batteries having improved properties such as higher electrolyte conductivities, more stable electrolytes, and the like. In particular, there is a need for thin film batteries whereby an intrinsic compressive stress of the electrolyte does not result in the formation of hillocks which may cause, for example, fracture of the anode film resulting in battery failure.